Problem: Simplify the following expression: $a = \dfrac{-7r - 3}{4r} \div \dfrac{1}{3}$
Answer: Dividing by a number is the same as multiplying by its inverse. $a = \dfrac{-7r - 3}{4r} \times \dfrac{3}{1}$ When multiplying fractions, we multiply the numerators and the denominators. $a = \dfrac{(-7r - 3) \times 3} {(4r) \times 1}$ $a = \dfrac{-21r - 9}{4r}$